1. Field of the Invention
The present invention pertains to gas flow meters, and more particularly, it pertains to gas flow meters of an electro-mechanical type wherein the differential pressure of gas flow through a pair of telescoping members elevates one of the members with the amount of such elevation being used as a gauge of the flow rate.
2. Description of the Prior Art
Gas flow meters as used by telephone companies provide some unique problems with regard to their construction. To prevent moisture damage to the individual telephone wires within the telephone cables, the cables are typically filled with dry air under pressure. In the event of a small break in the waterproof sheath surrounding the telephone wires, the pressurized dry air flows outwardly through the break preventing water penetration and continually drying the broken surfaces, but it is imperative that such leaks be detected and repaired early enough to prevent water damage to the cables and the telephone wires therein. Gas flow meters are thus used to measure the amount of gas flowing at many locations along the lengthy cable network and are continuously monitored in order to determine the location and severity of the break through which the air is leaking.
A long standing problem in the maintenance of such pressurized cable systems has been the search for a reliable low cost pressure meter for accurately sensing and indicating the relatively low rates of gas flow through such systems. Various transducers are available for measuring such gas flow through enclosed systems including devices which measure pressure drop across a structure presenting a known resistance to the flow of gas, rotation of a vane-like structure immersed in the gas, momentum transfer from the moving gas to a fixed body immersed therein, the positive displacement of pistons or nutating disks designed to allow a fixed volume of gas to pass from inlet to outlet during each compressive or rotational cycle of the piston or disk, and vertical displacement of a ball or other device moving upwardly within a transparent tube whose internal diameter increases with height and in which flow is directed upwardly (such device commonly being known as a "rotometer").
One particular type of flow meter which has been used for the reading of gas flow in pressurized cable systems is the telescoping member or floating piston type wherein flow through the meter creates a differential pressure to lift one member of a pair relative to the other thereby exposing an ever-increasing opening to the flow of gas. In such devices the amount of motion will be directly related to the amount of gas flow through the meter. For example, a device of such type is shown in my prior U.S. Pat. No. 4,528,858. As shown in this patent, the movable member may have an electrical contactor connected thereto to provide a continuous electrical signal to a remote monitor.
Another example of a variable area gas flow meter utilizing the floating piston or telescoping member construction is shown in prior U.S. Pat. No. 3,691,834 to deFasselle et al. In the meter disclosed in this patent, a floating piston contains an upper plate which is adapted to slide along a marked post thereby providing a visual reading of gas flow through the meter.
As shown in further prior patents to deFasselle et al, U.S. Pat. Nos. 4,489,614 and 4,787,253, the floating number may be connected to a sensing member so as to provide a continuous electrical output signal indicative of gas flow through the meter.